The present invention relates to a method and apparatus for combatting enemy helicopters which operate from a concealed position, emerging briefly and then using cover once again. The system according to the invention can be implemented even following loss of visual contact, using an electro-optical search head specially developed for helicopter-type recognition.
Various devices of this type are known. German Patent Document DE 37 33 681 C1, for example, discloses a device which uses a so-called infrared search head for helicopter detection. The search head consists essentially of an optical receiving arrangement in whose focal plane infrared-sensitive detector elements are arranged in a rectangular matrix. Each detector element can be read individually and the resultant signal investigated as to amplitude and frequency pattern.
The observation axis of the search head is directed vertically downward, since it is assumed that enemy helicopters move near the ground using the shelter of the terrain. The search head is designed so that it can reliably detect helicopters by reason of its visual field design and its height above the ground, based on their natural radiation, characteristically modulated by rotor blade movement, in a defined search area.
The design of the search head for the vertical observation direction limits considerably the operational performance of a defensive missile equipped with such a sensor, especially when the latter must be "shoulder fireable." Criteria for shoulder fireability are low weight (typically 12 kg), simple handling, high reliability, and a favorable cost-benefit ratio.
This sensor, which is directed vertically downward, can be used as follows in conjunction with a missile. When the observing shooter detects an enemy helicopter, he estimates the distance to the target and enters it into the missile launcher. Since the visual field of the sensor is limited, the success of the combat measure is critically dependent on the reliability of this estimate. In addition, assurance must be provided that the search areas established by the estimated values overlap. The missile is launched and, depending on the range and the predetermined visual field of the sensor, follows a preset flight path to a typical altitude of 800-1200 meters, where it is braked by a drogue chute. After the braking process is complete, the lengthwise axis of the missile is oriented vertically so that the target search head begins looking downward, and the search phase begins. The speed of fall must be adjusted by the chute to the performance of the signal evaluation method. When the target is acquired, the chute is released. The remaining part of the missile, containing the warhead, must now be accelerated from a slow falling speed so that the target itself can be reliably attacked at maximum flight speed.
The disadvantages of the above known device regarding efficiency of a weapon system are apparent:
False range estimates result in a miss, which can only be avoided by providing an additional laser rangefinder; PA1 The search phase takes place at low missile speed. During this time, the target can travel an additional distance, and overcoming this problem imposes increased demands on the target tracking speed of the missile; PA1 The unfavorable energy balance of the fuel consumption, which is increased by additional braking and accelerating maneuvers, results in an increase in weight and an unfavorable cost-benefit ratio; PA1 The chute increases both the complexity of the missile, (and hence its failure rate) and its manufacturing costs; and PA1 Without additional measures for electronic or mechanical image stabilization in the search head, the oscillating movements of the missile while suspended from the chute during the search phase cannot be compensated, so that the frequency of the helicopter radiation cannot really be detected at all, as stated in DE 37 33 681 C1.
An object of the present invention is to provide a simple and effective method and apparatus for reliably recognizing and attacking helicopters operating with concealment; in other words, without a visual link between the shooter and the target, without range measurement, and with a low missile weight. It is also important that the search for the target can take place when the flight profile is in a plane parallel to, or at a small angle of inclination to, the ground.
This and other objects and advantages are achieved by the missile guidance and tracking system according to the present invention in which the target search head of the missile is equipped with an optical lens system with two wedge shaped elements, at least one of which can be rotated relative to the other in order to adjust a line of sight axis of an optical image field thereof. After the missile is launched and rises to a predetermined altitude, it is then guided along an essentially horizontal flight path during a search phase in which the first and second wedge shaped optical elements are adjusted relative to each other in such a manner that the axis of the image field is directed downward toward the terrain passing beneath the missile. When the target helicopter is detected in the image field of the target search head, the missile enters a tracking phase in which it is guided downward to impact the target. For this purpose, the wedge shaped elements are rotated relative to one another to a position in which the image field of the target search head is directed along a longitudinal axis of the missile, and is aligned with the flight path. Information from the target search head is then used to guide the missile to target impact.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.